Technically understanding Airbag systems & SRS

This is a discussion on Technically understanding Airbag systems & SRS within Road Safety, part of the Team-BHP category; Originally Posted by ravib
Thanks so much for sharing this useful info @procrj. Truly appreciated !
IIRC, I have read ...

Thanks so much for sharing this useful info @procrj. Truly appreciated !
IIRC, I have read in other threads in TBHP that it is mandatory to wear seat belts in order for SRS Airbag to deploy (atleast in modern cars).

Aren't we getting mixed information ? Or Am i missing something.

I met with an accident last March in my i20 Asta. Because it was not a frontal impact, airbags did not get deployed, but we all walked out safely due to seat belts. However, when i dropped the car in Hyundai garage, i saw another i20 which had complete damage all the way till windshield due to head on collision. But the steering wheel was intact and Airbags didn't deploy because the driver was not wearing seat belts. This is my personal experience and confirmed by Hyundai service advisor.

-Ravi

That is incorrect. Airbags always deploy regardless of whether an occupant is wearing a seatbelt. I don't believe any manufacturer disables them if seatbelts are not worn. Sometimes airbags do not deploy due to various factors. They are not foolproof. There are countless instances reported where the airbags failed to deploy across all manufacturers and countries. It has nothing to do with seatbelts.

In any case, it is better to hit a soft airbag compared to impacting a hard steering wheel or windscreen. It is another story that a non belted person can slide off the airbag and hit other parts of the car. Of course it is imperative to wear seatbelts at all times.

....This may or may not trigger the restraint systems depending on case to case......This is again, very subjective.

Thank you vjkamal, for clearing up a moot point - however as you have clarified above, the discretionary nature of applying available technology (left to the policies of the car makers) is rather a case of safety chauvinism. After going through the thread, I for one will continue having misgivings about the efficacy of this system as it stands at present.

For our markets where most of the small cars have only twin airbags, it is the same at the input side except for the impact sensors which are absent at the sides and the outputs to the side and curtain airbags are absent. The backup capacitor shown in the block diagram is used to ensure that if the crash causes the battery power to be cutoff to the airbag system, the system will still work for a while until the capacitor discharges. This is usually around 5-10s after the battery power is cutoff, which is enough for the airbag circuit to do its job, store DTC and freeze frame data safely.

Keen to know to what the extent the safety systems in vehicles sold in India are adapted to our anthropometry (size, shape, even weight).

For example, a quick search on the Internet tells that average Indian male is at least 15 Kgs lighter and 6 inches shorter than their US counterparts, and even 5-7 Kgs lighter and 2 inches shorter than their Brazilian/Argentinian counterparts. This difference is likely to be of significance in the crash dynamics.

Any insights on how these global test bodies ensure their crash dummies are closely representing the average Indian will be helpful.

Sharing some bits from my side from the material I have:........The backup capacitor shown in the block diagram is used to ensure that if the crash causes the battery power to be cutoff to the airbag system, the system will still work for a while until the capacitor discharges......

Thanks audioholic, that is a most re-assuring bit of information! Even tho' air-bag deployment failures have been hitting the headlines with regularity in the recent past, it is re-assuring that certain bits of the system have been designed with due diligence. I still feel that the sensors (accelerometer/g-force sensors) could be designed with a greater degree of fail-safe reliability & sophistication. Smart phones do have very sensitive g-force sensors, but perhaps they are too fragile & delicate for the robustness needed for automotive use.

Any insights on how these global test bodies ensure their crash dummies are closely representing the average Indian will be helpful.

Talking only about the regulatory testing, most of the countries require the standard Hybrid III 50% dummy for the frontal impact tests. This dummy represents an average American adult male occupant that weighs around 78 kg and is 5 feet and 9 inches tall. In addition to this, US and EU require Hybrid III 5% dummies to comply with the criteria. This dummy represents an average American adult female occupant that weighs around 50 kg and is 5 feet tall.

For India, the regulation that will be followed is AIS098 which is indeed based on ECER94. This demands the tests to be done only with Hybrid III 50% dummy. As far as I know, there are no dummies designed purely based on an average Indian's anthropometry. However, some OEMs perform tests internally with different seat positions/ dummies to understand how the vehicle fares at different conditions.